The growth of gold nanoparticles by reduction by citrate and ascorbic acid has been examined in detail to explore the parameter space of reaction conditions. It is found that gold particles can be produced in a wide range of sizes, from 9 to 120 nm, with defined size distribution, following the earlier work of Turkevich and Frens. The reaction is initiated thermally or in comparison by UV irradiation, which results in similar final products. The kinetics of the extinction spectra show the multiple steps of primary and secondary clustering leading to polycrystallites.

Thermoelectric materials could play an increasing role for the effi cient use of energy resources and waste heat recovery in the future. The thermoelectric effi ciency of materials is described by the fi gure of merit ZT = ( S 2 σ T )/ κ ( S Seebeck coeffi cient, σ electrical conductivity, κ thermal conductivity, and T absolute temperature). In recent years, several groups worldwide have been able to experimentally prove the enhancement of the thermoelectric effi ciency by reduction of the thermal conductivity due to phonon blocking at nanostructured interfaces. This review addresses recent developments from thermoelectric model systems, e.g. nanowires, nanoscale meshes, and thermionic superlattices, up to nanograined bulk-materials. In particular, the progress of nanostructured silicon and related alloys as an emerging material in thermoelectrics is emphasized. Scalable synthesis approaches of high-performance thermoelectrics for high-temperature applications is discussed at the end. 714 Physical FunctionalityThe direct conversion of heat to electricity in thermoelectric devices is based on the Seebeck effect (named for Thomas J. Seebeck, 1821). In thermoelectric cooling devices use is made of the Peltier effect (named for Jean C. A. Peltier, 1834). [3][4][5] The thermoelectric effects were initially examined in metals. These generate only small thermovoltages of a few tens of microvolts per Kelvin. The electrical potential difference generated per degree of temperature difference is called Seebeck coeffi cient, S , or thermopower.By using semiconductors, substantially higher thermovoltages of some hundreds of μ V/K can be achieved. For thermoelectric applications, low bandgap semiconductors, with typical charge carrier concentrations in the order of 10 19 /cm 3 , are considered most suitable. Apart from a large Seebeck coeffi cient, a good thermoelectric material additionally needs to exhibit a high electrical conductivity and a low thermal conductivity to obtain a large fi gure of merit, ZT , at a certain temperature. The interdependence of these quantities has limited the ZT to values around one for the best conventional thermoelectric materials. For semiconductors and thermoelectric materials, the heat conductivity depends on both free charge carriers (holes or electrons) and phonons: κ tot = κ El + κ Ph . The phonon-based thermal conductivity κ Ph is decoupled from the electric conductivity. Thus, numerous attempts for the optimization of the thermoelectric effi ciency ZT in nanostructures are based on a reduction of the heat transport by phonons.

Current induced domain wall (DW) depinning of a narrow DW in out of plane magnetized ðPt=CoÞ 3 =Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism. DOI: 10.1103/PhysRevLett.101.216601 PACS numbers: 72.25.Ba, 75.60.Ch, 75.75.+a The recent discovery that a spin-polarized current can displace a domain wall (DW) through the spin transfer from conduction electrons to the local magnetization [1] has opened up an alternative approach to manipulate magnetization. Current induced domain wall motion (CIDM) has been investigated experimentally so far in detail in permalloy (Py; Ni 80 Fe 20 ) nanowires characterized by wide DWs (>100 nm) where the spin of a conduction electron is expected to follow adiabatically the magnetization direction as the electron passes across the DW [1,2]. A key question that has been raised is whether the spin transfer effect contains nonadiabatic contributions due to spin relaxation or nonadiabatic transport [2][3][4][5][6]. It was predicted [3,7] that from the efficiency of the spin transfer effect, which is measured by probing the dependence of the DW propagation magnetic field on the injected current, the nonadiabaticity can be deduced. However, in Py nanowires, the complicated 2D spin structures of the DWs prevent direct comparison to 1D models and a meaningful comparison to full 2D micromagnetic simulations is only possible if the exact spin structure during pulse injection is known, which is generally not the case. In particular, the wall deformations and transformations that have been observed [8] can render the results impossible to interpret in terms of the nonadiabaticity.To obtain simple DW spin structures, out-of-plane magnetized materials with a strong uniaxial anisotropy can be used where the simple Bloch or Néel DW spin structure is more apt for an analysis using an analytical 1D model including the nonadiabatic torque terms. In addition, a larger nonadiabaticity is expected in these materials due to the larger magnetization gradient for such narrow DWs [2,4,9]. This larger nonadiabaticity may explain the high efficiency of the current induced DW depinning reported recently in such materials [10,11]. However, another major obstacle for the determination of the nonadiabaticity from the dependence of the DW depinning magnetic field on current is that Joule heating strongly affects the thermally activated DW depinning. For experiments carried out at a constant cryostat temperature, it is thus hard to extract directly the contribution from the spin transfer torque.In this Letter we probe CIDM in out-of-plane magnetized ðPt=C...

Bi(2) Te(3) nanowires are of significant interest for two fields: nanostructured thermoelectrics and topological insulators. The vapor-liquid-solid method is employed in combination with annealing in a Te atmosphere, to obtain single-crystalline Bi(2) Te(3) nanowires with reproducible electronic transport properties (electrical conductivity and Seebeck coefficient) that are close to those of intrinsic bulk Bi(2) Te(3) .

We report time-resolved magneto-optic Kerr effect measurements of the longitudinal spin Seebeck